Welcome to the Weather Center

Members of Digi-Key’s Applications Engineering team began developing the Digi-Key Weather Center in a collaborative effort in February 2010. The Digi-Key Weather Center was placed on the roof of Digi-Key’s 600,000 square-foot facility in Thief River Falls, Minnesota in July 2010. The Digi-Key Weather Center was developed to demonstrate connectivity to customers by using products sold and supported by Digi-Key. Because Digi-Key is located in Northern Minnesota where the weather changes dramatically from summer to winter, it was determined to be the perfect location to demonstrate data communication with a weather station.

The primary device used to develop the Digi-Key Weather Center was a ConnectPort X4 Zigbee to Ethernet gateway, which is equipped with access to iDigi from Digi International, one of Digi-Key’s 440\+ franchised suppliers. Additionally, Digi International Series 2 XBee modules programmed with Zigbee firmware were used for wireless communication to the device sensors and gateway. The initial sensor board was designed around a Microchip PIC18F14K22 microcontroller and a VTI temperature/pressure sensor, both of which are housed in a sealed Bud boxes with an IP65 rating. Solar panels from Parallax and sealed lead acid batteries from B.B. Battery and Panasonic were also used to develop the Digi-Key Weather Center.

Digi-Key Applications Engineering team members Steve Dahl, Kevin Culkins, Shawn Rhen, Brandon Tougas, and Scott Raeker created the weather station, with each person assigned to different parts and stages of development. The project began with the design and construction of the structure that would hold the solar panel, control box and sensor nodes. Once the structure was completed, it was determined that sealed lead acid batteries and a charging circuit would be needed for power storage and distribution to the sensor nodes. The initial nodes developed for the project were a temperature/pressure sensor and a PWM controller enabled with a ZigBee module that relays the information to and from an Ethernet gateway. Next, python drivers were developed for the gateway, which relayed and managed the data to and from the sensor nodes. Finally, applications were developed for Android and Blackberry in order to present the data.

Telnet to the gateway using IP Address 192.168.1.xxx and port 23 then type

python dia.py

View the dia html page of the gateway by typing the following in a web browser

192.168.1.xxx/xxx

Control Box

The control box houses the the solar charging circuit board, battery, and the distribution of the power to the external sensors.

1st Gen Charger

The battery charger board uses a Texas Instruments BQ2031 lead-acid fast-charge IC. Circuitry is based on TI's DV2031S2 lead-acid charger development board and configured for a 6-cell battery using the two-step voltage charging algorithm. Fast (bulk) charge voltage is set for 14.9V and maintenance (float) voltage is set for 13.7V. The input power for the charger is provided by three solar panels (each one outputs approximately 20V @ 0.5A under full sunlight conditions).

3rd Gen Charger

(picture coming soon)

The latest revision of the charger implements a PIC30F6015 to control the output voltage of a LM2679 switching regulator circuit from National Semiconductor. The control software in the PIC results in a PWM output signal, which is delivered to the following circuit: The feedback signal is connected to the feedback pin of the LM2679. When the PWM signal is set to 0% duty, the PWM_LPF node is essentially driven to zero volts, which pulls the feedback node low through R20. This causes the regulator to respond by increasing it's output until the feedback pin reaches 1.21V. Conversely, if the PWM signal is set to 100% duty, the PWM_LPF node is driven to 3.3V, which pulls the feedback node high through R20. This causes the LM2679 to respond by decreasing the output until the feedback node reaches 1.21 volts. The output of the 10-bit resolution PWM allows ~4mV steps between 9.6V and 14V on the output of the LM2679. This provides very precise control of the voltage and current delivered to the 12v lead acid batteries.

The control algorithm in the dsPIC30F6015 charges the batteries according to a 3A system limit to 13.8 volts, and tracks the peak output power point of the solar panels. It also measures the current being consumed by each of the other nodes, and can individually disable them in case of high current draw or low battery voltage conditions.

Sensor Nodes

In order to decrease development time for sensor nodes and Python drivers for the gateway, a common format for passing data has been created and standardized. This will also reduce the amount of data being passed between the Gateway and the XBee enabled sensor nodes.

Gateway Character Key:

request = "R" - All requests will lead with a NULL (0x00) operator which is used by sleeping nodes for wakeup on UART. hello = "H"

Voltage regulation is provided by a V-Infinity DC/DC converter, V7803-500. The form factor and performance level makes the V78XX series a drop-in replacement for any LM78xx linear regulator in TO220 packaging.

The #40R Anemometer is a three-cup design with a dry contact reed switch sensor. Frequency is proportional to cup rotational speed..

Camera

Beagleboard xM

Logitech UVC Camera

Atheros USB WiFi (5Ghz)

Installation Details: [[Weather Center Camera]]

Light/Humidity/Supply Voltage/Temperature

The PIC24FJ192GA110 MCU was used for a weather node to return wireless readings of temperature, humidity, Supply Volatage and Lux (luminous flux density). For Lux sensing, a Microsemi Lux sensor LX1971IDU was used due to its temperature stability and approximate human eye spectral response. For the humidity measurements, a Honeywell HIH-5031 humidity sensor 480-3284-1-ND was employed. This sensor was chosen since it has a relative humidity operational range of 0 to 100% with a low hysteresis of +/- 3%. The temperature was measured using a Microchip TC1047AVNBCT temperature sensor. Hardening the unit for inclement weather was a must. For this a NEMA certified enclosure 377-1459 and C&K sealed IP67 rated tactile pushbutton switches CKN10004 were used.

Solar Power

Currently 3, 18V @ 10W, Solar Panels from Parallax Inc, 750-00032-ND are used for power generation on this Weather Station.

Structure

The Electronic enclosures used in this project are from Bud Industries. The Main box is BUD's NBA series, 377-1139-ND. This box is rated at IP65 of IEC 529 and NEMA 1, 2, 4 and 4x specifications. Temp range is -40c to +70c. This Box does not have an outdoor rating but has healed up very well to the Northern Minnesota environment... It has seen near 100deg F in the summer and this winter it has seen -38F with no problems. To provide venting to the box we installed Buds NBX-10910-ND and the NBX-10911-ND moisture vents, one on each end. These vents have worked very well in venting the box and to this point we have not detected any snow or moisture migration into the box. To interface the box to the sensors we used Switchcrafts SC1391-ND Jack and the SC1381-ND Plug. These connectors are rated at IP68 but take note, only when they are properly mated. The jack is not sealed on the inside so if you do not have anything plugged in to the jack be sure to use the "JCAP" SC1396-ND to seal the Jack when not in use. On the inside of the box we installed Injectorall Electrics FR4 un-clad board material to make the back panel PC8-UNCLAD-ND. On the panel we installed the primary circuit board and two power distribution strips by Molex WM5737-ND.

Junction Box

July 30th, 2010 a junction box was added to the weather station for future solar panel expansion. The connectors used are Switchcraft's Sealed Power 761KSxx plugs (Digi-Key part# SC1382-ND) and L712AS jacks (Digi-Key part# SC1390-ND). These connectors are IP68 and NEMA 250 (6P) rated with J-Cap plugs Digi-Key part# SC1396-ND) used to seal unused jacks. The box used is a Bud Industries "AN" series (Digi-Key part# 377-1429-ND) which is IP65, IP66, IP67, NEMA 1,2,4,4X,12,13, UL-508 rated. Image Update: The junction box was modified by replacing the Schottky diodes with "Super Barrier" SBR2U30P1 diodes from Zetex Diodes (Digi-Key part# SBR2U30P1DICT-ND). The Super Barrier diodes have ultra low forward voltage drop of 0.4V maximum at 2.0A..

5 Comments

I have the same development board (DV2031S2) driven by a 15W SolarPanel, 6 cell configuration, charging a +12V LeadAcid Battery. The DV2031 datasheets states minimum 22VDC (SolarPanel) for 6 cell config. On full sun days it performs, but on gray, cloudy, snow days it does not. I noticed the implementation of 3rd Gen Charger and would like more information, perhaps this would improve my system performance.

The third gen charger consists of an MCU (Microchip this time) measuring the solar voltage and current, battery voltage and current, and load current, and "influencing" the feedback circuit of a National (TI) LM2679 switching buck regulator through a DAC and a buffer amp. This allows the MCU to control the output voltage (and thus current) of the switching regulator and output a constant current, constant voltage, or a floating voltage to the batteries, as well as run a basic solar MPPT algorithm. There is also a bank of ultracapacitors in parallel with the solar panels to smooth out the ripple as clouds pass by.

Not sure of the exact issues Gen1 had, it was before my time here. Rumor has it that it struggled with clouds and snow too.

Throwing up an EEWiki page on that project is somewhere on a back burner. The code isn't complete yet; just enough to charge the batteries and report stats on a wireless link. We've been working on getting the weather center data back online, and once that happens, I'll likely make the time to connect the charger to the ZigBee network, finish the code, and post the project here.